Projection system



June 28, 1960 w. E. GLENN, JR 2,943,147

PROJECTION SYSTEM Filed Jan. 13, 1958 E lecfron Gun 37 I Screen /n me n for William E, Glenn, J/'.,

His Attorney.

United States Patent PROJECTION SYSTEM William E. Glenn, Jr., Scotia, N.Y., assignor to General Electric Company, a corporation of New York Filed Ian. 13, 1958, Ser. No. 708,528

7 Claims. (Cl. 178-75) The present invention relates to a projection system of the type utilizing a deformable medium, and more particularly to the use of a deformable medium therein.

In Eidophor systems, and in other types of projection television systems, an electron beam that is velocity modulated by a television signal is deflected over the surface of a. high resistivity, deformable medium which is usually a liquid or a gelatin. Electrons from the beam, which are electrostatically attracted to a conducting coating beneath the medium, press on the surface of the deformable medium to produce deformations the amplitudes of which correspond to the instantaneous amplitude of the television, signal when the respective deformations were formed. This deformable medium is placed in a suitable light and optical system wherein the deformations phase ditfract light to produce a viewable image the intensity of which is a function of the amplitudes of the deforma tions and thus also a function of the applied television signal.

7 Prior materials utilized for the deformable medium have, decreased to zero thickness after being subjected to the pressure of the electrons for a short period of time and thus had to be periodically replaced so that the medium had sufficient thickness to produce deformations of the desired amplitudes. Obviously, it would be advantageous to obviate theneed for periodically replacing the'medium. I

Accordingly, an object of the present invention is to provide a projection system in which the deformable medium does not decrease to zero thickness under pressure of electrons.

,Anotherobject is the use in projection systems of a deformable'medium' that maintains its thickness independently of the length of time it is subjected to pressure by electrons.

These and other objects are achieved in one embodiment of my invention which comprises a projection system in which I use a deformable medium having a resistivity that decreases with decreases in thickness of the medium.

The novel features believed characteristics of the invention are set forth in the appended claims. The invention itself, together with further objects and advantages thereof, may best be understood by reference to the following description, taken in connection with the accompanying drawing in which the single figure illustrates a typical projection television system.

Referring to the figure, I have illustrated an electron gun 11 for producing an electron beam 13 and deflecting it in a rectangular raster over the surface of a transparent deformable medium 15 that is within a transparent container 17. Beam 13 is preferably velocity modulated by a television signal that is applied to the deflection means (not shown) in electron gun 11.

Deformable medium 15 has a center portion 19 of decreased thickness, coincident with the raster area of beam 13, which is produced by electrons from beam 13 that are attracted to a conducting coating 21 on the inner surface of container 17. These electrons also produce deformations in the surface of medium 15, the amplitudes of which are a function of the number of electrons deposited by beam 13 at the various points on the surface of medium 15. Consequently, the amplitudes of these deformations are a function of the television signal modulating electron beam 13.

These deformations are utilized to diifract light from a light source 23 in an optical system which is illustrated as including a lens 24 that images light source 23 on the surface of medium 15 through a bar and slit system 25. Another lens 29 images the slits of system 25 on the bars of another bar and slit system 31 in the absence of deformations in the surface of medium 15. However, any deformations phase diffract the light so that it passes through the slits in system 31 with an intensity that corresponds to the amplitudes of the deformations and thus the amplitudes of the applied television signal. The light passing through system 29 is imaged by a projection lens 33 on a screen 35 after reflection from a mirror 37.

If a conventional deformable medium is utilized in the illustrated system, the average charge density produces a force on medium 15 that overcomes the surface tension from the excess medium outside the raster area and decreases the portion 19 of medium 15 to zero thickness. Then, of course, no deformations can be formed and the system becomes inoperative until medium 15 is replaced.

I have discovered that if medium 15 has the property of decreasing in resistivity with decreasing thickness, portion 19 does not decrease to zero thickness under the pressure of the charges but rather maintains a thickness the value of which is a function of the magnitude of charge density on the surface of medium 15. With a decrease in resistivity, the time constant is decreased for the passage of leakage current from the surface of medium 15 to the conducting coating 21 beneath it. The resulting increase in leakage current decreases the charge den sity on the surface of medium 15 thereby relieving the pressure to some degree. Eventually, an equilibrium condition is attained 'in which the pressure from the charges on the surface of medium 15 equals the pressure from the surface tension on the excess medium around the raster. Then the thickness at this equilibrium condition is maintained. Of course, the charge density on the surface of medium 15 never decreases to zero due to the leakage because it is continually replaced by the electrons from beam 1 3.

Many of the requirements for medium 15 are the same as for prior art mediums. For example, it must be transparent, be capable of withstanding electron bombardment without significant decomposition, have a viscosity that for the operating temperature, which will probably be between 25 C. and C., of approximately 100 to 50,000 centistokes, and, of course, it must not decompose the conducting coating 21.

In addition to those prior art requirements the medium 15 of the present invention should have a resistivity that varies within the range of approximately 10 to 10 ohms-cm, with the average resistivity at the stable thickness being approximately 10 ohms-cm. Following is a list of some of the materials that satisfy these requirements:

(1) Butyl esters of methyl- 3-carboxyethylsiloxanes.

(2) Beeswax.

(3) Methyl silicone fluids.

(4) Methyl silicone fluids containing up to about 5% of phenyl silicones.

(5) Methylphenyl silicones containing an average of 2 methyl and phenyl groups per silicon atom in which the mole ratio of methyl groups to silicon atoms is greater than 0 and less than 2.0.

Specific materials within the above list which have been found particularly useful are a viscosity at 25 C. of 1,000 centipoises and consisting of recurring siloxane units, each of which is the butyl ester of methyl-p-carboxyethyl siloxane; a methyl silicone fluid having a viscosity at 25 C. of 5,000 centistokes; and a methyl phenyl silicone having a viscosity of 175 centistokes at 25 C. and containing 1.1,methyl groups and 0.9 phenyl group per silicon atom.

Although I have described my invention with respect to a transmission type projection television system in which light passes through container 17, it should be apparent to those skilled in the art that it is equally applicable with a reflection type transmission system in which the light is reflected from the coating 21. Then of course coating Zllhas to be a reflecting material such as aluminum. I

Although the invention has been described WiiZh'IGSPBCt to certain specific embodiments, it will be appreciated that many modifications and changes may be made by those skilled in the art without departing from the spirit of my invention. I intend, therefore, by the appended claims, to cover all such modifications and changes as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. A projection system comprising a container having a conducting interior, a deformable medium in said container that decreases in resistivity with decreases in thickness and in the presence of an electrical charge on the surface thereof, an electron beam means for producing an electrical charge on the surface of said deformable medium as a function of an applied electrical signal and cooperating with said conducting interior to subject the medium to a deforming force to produce deformations in the surface of said medium, and a light and optical system for projecting light as a function of the deformations in the surface of said medium.

2. The projection system as defined in claim 1 wherein the average volume resistivity of said deformable medium varies within the range of to 10 ohms-cm.

3. The projection system as defined in claim 1 wherein said deformable medium is selected from the group consisting of methyl silicone fluids. and beeswax.

' 4. A projection system comprising adeformable light modulating medium that decreases in resistivity with decreases in thickness in the presence of an electrical charge silicone fluid having a 4 r substantially constant potential in association with said deformable light modulating medium whereby the particles of charge in the charge pattern on the surface of said deformable light modulating medium are attracted to said element to produce deformations in the surface of said medium, and a light and optical system for projecting light as a function of the deformations in the surface of said medium.

5. The system as defined in claim 4 wherein said deformable light modulating medium decreases in average volume resistivity within the range of 10 to 10 'ohmscm. with decreases in thickness.

6. A projection system comprising a deformable me dium having a resistivity that varieswith the thickness of surface of said medium that in electrically reacting with said conducting plane produces deformations in the surface of said medium, the resistivity of said medium varying with the medium thickness in the presence of electrical charge on the surface thereof such that the surface tension of said medium andthe force resulting from the reaction of said electrical charge and said conducting plane reach a condition of equilibrium such that the thickness ofsaid medium is maintained, and a light and optical system for projecting light as a function of the deformations in the surface of said medium. 7

7. A projection system comprising a deformable light modulating medium the resistivity of which decreases with decreases in thickness of said medium in the presence dium, an element for establishing-a region of substantially on the surface thereof, an electron beam means for producing a charge pattern on the surface of said deformable light modulating medium as a function of applied signals, means including an element for establishing a region of constant potential in association with said deformable light modulating medium whereby the particles of charge in the charge pattern on the surface of said deformable light modulating medium are attracted to said element to produce deformations in the surface of said medium, the

volume resistivity of said medium varying with the medium thickness such that the surface tension of said medium and the force of said electrical charge cooperating with said element reach a condition of equilibrium such that the thickness of said medium is maintained, and a light and optical system for projecting light as a function of the deformations in the surface ofsaid medium.

References Cited in the file of this patent UNITED STATES PATENTS 2,605,352 Fischer July 29,1952 

